Vertical tubular furnace for high operating pressures

ABSTRACT

A cylindrical elongated electric furnace placed in a pressure chamber for isostatic compression with its longitudinal axis substantially vertical. A heat-insulating mantle is provided for thermal isolation of the hot furnace chamber from the walls of the pressure chamber. This mantle is constructed of thin sheet metal arranged on a tubular frame and is free from insulating material of ceramic type. The sheet metal forms a plurality of cylindrical or conical layers located radially one outside the other and having gas-filled spaces between them.

United States Patent 1 [111 3,752,456 Larker I Aug. 14, 1973 [54] VERTICAL TUBULAR FURNACE FOR HIGH 3,433,618 4/l969 Seelandt 263/40 R OPERATING PRESSURES 3,456,935 7/1969 Bornor 263/40 R [75] Inventor: Hans Larker, Robertsfors, Sweden Primary Examiner john l camby [73] Assignee: Allmanna Svenska Elektriska Attorney-Jennings y,

Aktiebolaget, Vasteras, Sweden 22 Filed: Mar. 1, 1972 [57] ABSTRACT A cylindrical elongated electric furnace placed in a Appl' 230,898 pressure chamber for isostatic compression with its longitudinal axis substantially vertical. A heat-insulating [3 Foreign Application Priority Dat mantle is provided for thermal isolation of the hot furnace chamber from the walls of the pressure chamber. Mar. 15, Sweden.. mantle i constructed of h n hee mew a ranged on a tubular frame and is free from insulating material [52] US. Cl. 263/40 R, 13/31, 263/50 of ceramic type The sheet metal forms a plurality of [51] Int. Cl- F27!) 3/02 cylindrical or conical layers located radially one our [58] Field Of Search 263/40 R, 50; 13/31 side the other and having g u spaces between them. [56] References Cited UNITED STATES PATENTS 8 Claims 7 Drawing Figures 3,317,203 5/ 1967 Lin et al 263/50 VERTICAL TUBULAR FURNACE FOR HIGH OPERATING PRESSURES BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylindrical elongated furnace, preferably vertical, for simultaneous treatment of material at high pressure, preferably 500 bars and above, and high temperature, up to about 1,500C. An extremely important element in the furnace is the heat-insulating mantle which thermally isolates the hot furnace chamber from the walls of the surrounding pressure chamber, which chamber takes up the forces generated by the compressed gas enclosed in the furnace and which must therefore be kept cool, possibly by forced cooling. When the furnace is heated, the surface of the insulating mantle facing the furnace chamber will be heated to l,300C, for example, whereas its outwardly facing surface which is close to the wall of the pressure chamber and cooled by this wall is only heated to 50 or 100C. Argon is usually used as pressure medium. At the high pressure used, argon has very high density but at the same time very low viscosity, only 4 times that of air at atmospheric pressure, and it is therefore extremely mobile. Since with respect to its density the gas also has considerable heat capacity it is important that the insulation surrounding the actual furnace chamber be constructed in such a way that the least possible convection is obtained between the furnace chamber itself and the inner walls of the pressure chamber so that the heat losses will not be unreasonably great. The decrease in convection also results in the temperature distribution in the longitudinal direction of the furnace becoming more uniform.

2. The Prior Art Satisfactory heat-insulating properties for furnaces in this particular field have been obtained by constructing the insulation in the manner shown in US. Pat. No. 3,470,303.

SUMMARY OF THE INVENTION The object of the present invention is to achieve an improvement of this previously known type of insulation with the help of which the insulation properties will not deteriorate even after a long time in operation. The insulation should also be relatively simple to make using economic manufacturing methods. This is achieved by means of an insulation constructed of sheet metal forming a plurality of surfaces of revolution (cylindrical or conical) on a tubular frame and having gas-filled spaces between them communicating at least at their bottoms with the space outside the mantle. A purely metallic insulation of the furnace chamber from the walls of the pressure chamber is therefore obtained. Such an insulation is extremely effective, and, since it is free from insulating material of ceramic type, its

heat-insulating properties will be stable as an insulation of this type cannot deteriorate because of alterations in volume and cracking.

The insulating mantle can be constructed in many different ways. For example it may with advantage consist of a plurality of truncated cones made of metal foil which are slipped onto the tubular frame and attached to the frame at the upper edges of the cones. Another suitable method of effecting an insulation according to the present invention is to wind on metal foil in the form of a strip with an irregular edge'and attach this to the frame along a substantially helical line, for example by welding.

The irregular edge of the strip can be achieved by rolling, for example, or by other suitable methods as will be clear from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further described with reference to the accompanying drawings showing different embodiments by way of example.

FIG. 1 shows schematically a section of a furnace according to the invention, placed in a pressure chamber for isostatic compression.

FIG. 2 shows a first embodiment of a mantle insulation intended for this furnace.

FIGS. 3 and 4 show a second embodiment of such an insulation and how it is manufactured.

FIGS. 5 and 6 show two different ways of obtaining a metal strip for manufacturing the insulation in accordance with FIG. 3.

FIG. 7 shows finally a third embodiment of a mantle insulation according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The pressure chamber 1 in FIG. 1 consists of a'thickwalled cylindrical steel tube 2, around which a wire mantle 3 of cold-rolled high-strength steel wire has been wound under pre-stressing. During the winding such great radial and tangential compressive stress are achieved in the tube wall that the cylindercan withstand an internal over-pressure of more than 3,000 bars. Argon is used as pressure gas. The wire mantle 3 is water cooled. The ends of the cylinder are sealed at the bottom by a plug 4 and at the top by a threaded lid 5. The bottom plug 4 carries the furnace insert 6 placed in the pressure chamber 1 and is provided with lead-ins, f

not shown, for electric current to the furnace, a lead-in for thermoelement cables and a pipe-inlet for the compressed gas. The furnace 6 has a furnace chamber 7 in which electrical heating elements 8 are arranged. The furnace chamber 7 is provided with heat insulation comprising a surrounding annular insulation mantle 9, a bottom part 10 and a lid 11. The insulation parts 9', l0 and 11 prevent convection from the furnace chamber 7 to the annular gap 20 between the insulation mantle 9 and the walls of the pressure chamber 1.

The insulation mantle 9 is constructed of metal foil having a thickness of 0.01 0.1 mm. FIG. 2 shows an example of how such insulation can be constructed. A

tion according to the invention, the manufacturing of which is illustrated in FIG. 4. This insulation is obtained by a strip 15 which has been given an irregular edge by rolling, for example, being wound on and attached (welded) to the tube 13. The insulation mantle may be dimensioned in .the following way, for example (see the designations in FIG. 4): t 30 mm, r l50 mm, b

200 mm, s mm. Twenty layers are thus obtained with a radial spacing of 1.5 mm.

Besides being rolled, the irregular edged strip can be obtained by folding the edge of the strip as shown in FIG. 5. Another possibility is shown in FIG. 6. An originally straight strip is here divided by cutting a number of trapezium-shaped parts A, B, C, D, E, and so on, alternate parts ED and so on, for example, being inverted and the parts then joined by means of welding, for example.

FIG. 7 shows finally a third embodiment of an insulation mantle according to the present invention. This mantle is wound from metal foil 16 having the same width as the height of the insulation mantle. The various layers are spaced-from each other with the help of narrow metal strips 17, for example 1 mm'in thickness, serving as spacer elements. The stack obtained in this way is held together by rivets l8 distributed around the circumference of the mantle. In order to stabilize the stack one or more sheet metal cylinders 19 may be arranged in the mantle. Each metal strip 17 extends through only a part of the thickness of the insulation mantle and the various strips are displaced in relation to each other in the axial direction of the mantle so that no coherent heat-conducting bridges are formed between the two sides of the insulating mantle.

The insulation mantle shown in FIG. 7 need not be wound from one or more strips 16 in several layers. Instead it may consist of several coaxial cylinders made of metal foil between which substantially closed annular spaces are formed.

As examples of materials which are suitable for use in the insulation mantle may be mentioned austenitic stainless steel, heat-resistant material with an Ni base (Inconnel, Hastelloy), molybdenum, tungsten or a combination of two or more of these materials.

I claim:

1. Cylindrical elongated furnace for treating material at high temperature in a gaseous atmosphere which is under high pressure, the furnace (6) being positioned in a pressure chamber (1) with the longitudinal axis of the furnace directedsubstantially vertically, said furnace (6) containing a furnace chamber (7) provided with heating elements (8), a heat-insulating sheath enclosing the furnace chamber comprising an insulating mantle (9') with an insulating lid (11) and an insulating bottom (10), in which at least the innermost part of the heat-insulating mantle (9) comprises a tubular frame (13) and thin sheet metal on the tubular frame (13) forminga plurality of layers shaped as'surfaces of revolution located radially one outside the other and having gas-filled spaces (14) between them, said spaces extending substantially in the longitudinal direction of the furnace (6) and communicating with the space outside the tubular frame at the lower parts of the spaces (14).

2. Furnace according to claim 1, in which the thin sheet metal is a metal foil having athickness of 0.1 mm at the most.

3. Furnace according to claim 1, in which the sheet metal is constructed of a plurality of truncated cones (12) made of metal foil which surround the tubular frame l3) and are arranged one above the other with the cone apex pointing upwardly, the upper edges of the cones (12) being attached to the frame (13).

4. Furnace according to claim 1, in which the sheet metal is a metal foil in the form of a strip (15) with irregular edges which is wound around the frame (13) and attached to the frame along the upper edge of the strip 15) following a substantially helical line.

5. Furnace according to claim 4, in which the metal foil (12,15) is attached to the frame (13) by welding.

6. Furnace according to claim 1, in which the strip (15) with irregular edges is formed by rolling.

7. Furnace according to claim 4, in which the strip 15) with irregular edges is shaped by folding together one edge of an originally straight strip.

8. Furnace according to claim 4, in which the strip (15) with irregular edges is composed of a plurality of joined trapezium-shaped pieces. 

1. Cylindrical elongated furnace for treating material at high temperature in a gaseous atmosphere which is under high pressure, the furnace (6) being positioned in a pressure chamber (1) with the longitudinal axis of the furnace directed substantially vertically, said furnace (6) containing a furnace chamber (7) provided with heating elements (8), a heat-insulating sheath enclosing the furnace chamber comprising an insulating mantle (9) with an insulating lid (11) and an insulating bottom (10), in which at least the innermost part of the heat-insulating mantle (9) comprises a tubular frame (13) and thin sheet metal on the tubular frame (13) forming a plurality of layers shaped as surfaces of revolution located radially one outside the other and having gas-filled spaces (14) between them, said spaces extending substantially in the longitudinal direction of the furnace (6) and communicating with the space outside the tubular frame at the lower parts of the spaces (14).
 2. Furnace according to claim 1, in which the thin sheet metal is a metal foil having a thickness of 0.1 mm at the most.
 3. Furnace according to claim 1, in which the sheet metal is constructed of a plurality of truncated cones (12) made of metal foil which surround the tubular frame (13) and are arranged one above the other with the cone apex pointing upwardly, the upper edges of the cones (12) being attached to the frame (13).
 4. Furnace according to claim 1, in which the sheet metal is a metal foil in the form of a strip (15) with irregular edges which is wound around the frame (13) and attached to the frame along the upper edge of the strip (15) following a substantially helical line.
 5. Furnace according to claim 4, in which the metal foil (12,15) is attached to the frame (13) by welding.
 6. Furnace according to claim 1, in which the strip (15) with irregular edges is formed by rolling.
 7. Furnace according to claim 4, in which the strip (15) with irregular edges is shaped by folding together one edge of an originally straight strip.
 8. Furnace according to claim 4, in which the strip (15) with irregular edges is composed of a plurality of joined trapezium-shaped pieces. 